The rare find in Bull’s Wood, a Suffolk Wildlife Trust reserve near Bury St Edmunds, is particularly significant in that it is believed to be entirely separate from existing colonies.

Mammal expert Simone Bullion, senior conservation officer at the Trust, said although Bull’s Wood has long been connected with dormice, with documentary evidence of nest sites stretching back to 1885, searches in the early 2000s proved fruitless.

But following funding from the SITA Trust and a predictive mapping project a nest was found in a nest tube late last year. Dr Bullion explained: “By combining those two features to narrow down what is very much a needle in a haystack to find a remaining dormouse population. Although we have found quite a number of new populations in the last couple of years, all of them bar one were actually satellite populations to known existing populations.”

The Bull’s Wood site is two kilometres away from Bradfield Woods, where dormice are now thriving after being introduced in 2006. Dr Bullion said work was now underway to find out the extent of the population and protect them in the face of countrywide habitat fragmentation. Measures could include planting hedges to strengthen links between Bull’s Wood and Bradfield.

Dr Bullion added: “We’re looking into the long term to ensure that the population is there for another 100 years or so.”